Warsaw breakage syndrome, a cohesinopathy associated with mutations in the XPD helicase family member DDX11/ChlR1

Abstract

The iron-sulfur-containing DNA helicases XPD, FANCJ, DDX11, and RTEL represent a small subclass of superfamily 2 helicases. XPD and FANCJ have been connected to the genetic instability syndromes xeroderma pigmentosum and Fanconi anemia. Here, we report a human individual with biallelic mutations in DDX11. Defective DDX11 is associated with a unique cellular phenotype in which features of Fanconi anemia (drug-induced chromosomal breakage) and Roberts syndrome (sister chromatid cohesion defects) coexist. The DDX11-deficient patient represents another cohesinopathy, besides Cornelia de Lange syndrome and Roberts syndrome, and shows that DDX11 functions at the interface between DNA repair and sister chromatid cohesion.

Figure 1

Characteristics of the Affected Individual The patient is a male from Warsaw, Poland, with severe intrauterine growth retardation (weight 1300 g [< 3^rd centile], length 38 cm [< 3^rd centile ], and head circumference 25 cm [< 3^rd centile] at 37 wks of gestation). Several congenital abnormalities were found, including microcephaly, facial dysmorphy (small and elongated face, narrow bifrontal diameter, jugular hypoplasia, bilateral epicanthal folds, relatively large mouth, and cup-shaped ears), high arched palate, coloboma of the right optic disc, deafness due to structural abnormalities of the inner ear (bilateral hypoplastic cochlea), small ventricular septal defect, bilateral clinodactyly of the fifth fingers, syndactyly of the second and third toes, cutis marmorata, and one hypo- and three hyperpigmented patches on the skin. Psychomotor and mental development were mildly retarded. Growth was severely retarded (Figure S1). Genitalia and pubertal development were normal. No malabsorption or pituitary or thyroid insufficiency was found. No hematological abnormalities, immunodeficiency, or malignancy were noted either.

Figure 2

Chromosomal Breakage and Cohesion Defects in Cells Derived from the Affected Individual (A) Chromosomal breakage after MMC treatment of T lymphocyte cultures from the affected individual (VU1202), his mother, a healthy control, and an individual with Fanconi anemia. Percentages of cells with up to ≥ 10 break events per cell are indicated. (B) Representative pictures of metaphases with railroad chromosomes (RR) and total premature chromatid separation (PCS). (C) RR and PCS are frequently observed in lymphoblasts from an individual with Roberts syndrome and in those from the affected individual. Percentages of cells with normal chromosomes, RR, and PCS are shown in untreated cells and in cells treated for 48 hr with 150 nM MMC (M) or 2.5 nM camptothecin (C). Patient VU1177 is homozygous for c.1105insA in ESCO2, and patient HSC72 is homozygous for a deletion of exon18 to 28 in FANCA. The figure shows the average of two experiments with standard deviation.

Figure 3

DDX11 Mutations in the Affected Individual and His Parents (A) Immunoblotting revealed normal ESCO1 and ESCO2 but hardly detectable DDX11 protein levels in lymphoblasts (VU1202-L) and fibroblasts (VU1202-F) from the affected individual. (B) Sequence analysis on genomic DNA revealed the splice-site mutation IVS22+2T>C in the DDX11 gene of the affected individual and his mother (red arrow). In the paternal allele, a 3 bp deletion was found (red arrow), which deleted a conserved lysine residue (K897) from the DDX11 protein. (C) Sequencing on cDNA of the affected individual showed that the splice-site mutation IVS22+2T>C leads to a 10 bp deletion of exon 22 sequence from the DDX11 cDNA, resulting in a frameshift at codon 754 and a premature stop at codon 763.

Figure 4

DDX11 Deficiency Underlies the Abnormal Cellular Phenotype in the Affected Individual (A–D) Two independent transfections of DDX11 cDNA into lymphoblasts of patient VU1202 (A) restored normal DDX11 protein levels and chromosomal cohesion defects (B), as well as hypersensitivity to growth inhibition by MMC (C) and camptothecin (D). (C) and (D) show the average of two independent experiments, with the standard error of the mean shown.

Figure 5

Pedigree of the Affected Individual and Cancer Incidence in the Family (A) Pedigree of the affected individual (V:3). The mother of the patient (IV:2) had two miscarriages in the first trimester (V:1 and V:2) and developed Hodgkin lymphoma (HL) at age 33. The patient's grandmother (III:2), also a carrier of the splice-site mutation IVS22+2T>C, was diagnosed with an adenocarcinoma of the endometrium (AE) at the age of 62. The patient's great-grandmother (II:2) was diagnosed with cervical cancer (CC) at age 56, and her sister (II:3) was diagnosed with uterine cancer (UC). Of the latter two cases, the DDX11 mutation status is unknown. There is no evidence for cancer predisposition in the family of the father. (B) The splice-site mutation IVS22+2T>C was detected in the tumors of the mother and grandmother.